1. Field of the Invention
This invention relates to driving method and apparatus for a plasma display panel, and more particularly to driving method and apparatus for a plasma display panel wherein a gray scale leves are linearized.
2. Description of the Related Art
Generally, a plasma display panel(PDP) radiates a Phosphor by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. The PDP is largely classified into a direct current(DC) driving system and an alternating current(AC) driving system.
The PDP of AC driving system is expected to be highlighted into a future display device because it has advantages in the low voltage drive and a prolonged life in comparison to the PDP of DC driving system. Also, the PDP of alternating current driving system allows an alternating voltage signal to be applied between electrodes having dielectric layer therebetween to generate a discharge every half-period of the signal, thereby displaying a picture. The AC-type PDP makes a memory effect because it uses a dielectric material into the surface of which a wall charge is accumulated during the discharge.
Referring to FIG. 1, the AC-type PDP includes a front substrate 1 provided with a sustaining electrode pair 10, and a rear substrate 2 provided with address electrodes 4. The front substrate 1 and the rear substrate 2 are spaced, in parallel to each other, with having a barrier rib 3 therebetween. A mixture gas such as Nexe2x88x92Xe or Hexe2x88x92Xe, etc. is injected into a discharge space defined by the front substrate 1 and the rear substrate 2 and the barrier rib 3. Any one of the sustaining electrode pair 10 is used as a scanning/sustaining electrode that responds to a scanning pulse to cause an opposite discharge along with the address electrodes 4 and responds to a sustaining pulse to cause a surface discharge along with the opposite sustaining electrode 10. Also, the sustaining electrode 10 opposed to the sustaining electrode 10 used as the scanning/sustaining electrode are used as a common sustaining electrode to which a sustaining pulse is applied commonly. On the front substrate 1 provided with the sustaining electrode pair 10, a dielectric layer 8 and a protective layer 9 are disposed. The dielectric layer 8 is responsible for limiting a plasma discharge current as well as accumulating a wall charge during the discharge. The protective film 9 prevents a damage of the dielectric layer 8 caused by a sputtering generated during the plasma discharge and improves an emission efficiency of secondary electrons. This protective film 9 is usually made from MgO. Barrier ribs 3 for dividing the discharge space is extended perpendicularly at the rear substrate 2. On the surfaces of the rear substrate 2 and the barrier ribs 3 is provided a phosphor layer 5 which is excited by a vacuum ultraviolet lay to generate a visible light.
In such a PDP, one frame consists of a plurality of sub-fields and a gray level is expressed by a combination of the sub-fields. For instance, if it is intended to display a picture by 256 gray levels, then one frame interval (i.e., 16.67 ms) is time-divided into 8 sub-fields as shown in FIG. 2. Each of these 8 sub-fields is again divided into a reset interval, an address interval and a sustaining interval. In the reset interval, the full screen is initialized. In the address interval, discharge cells on which a data is to be displayed are selected by the address discharge. The selected discharge cells sustain the discharge in the sustaining interval. Herein, the reset interval and the address interval of each sub-field are same every sub-field, whereas the sustaining interval of each sub-field is assigned to be increased at a ratio of 2n(n=0, 1, 2, 3, 4, 5, 6, 7) at each sub-field in accordance with a relative brightness ratio. Since the sustaining interval becomes different at each sub-field as mentioned above, the sustaining interval of each sub-field, that is, a sustaining discharge frequency is controlled to express a gray level of picture.
Referring to FIG. 3, in the reset interval, a screen is initialized by a reset pulse applied between an address electrode(X) and a common sustaining electrode(Z). In the address interval, a data is supplied to the address electrode(X) and a scanning pulse synchronized with the data is sequentially applied to the scanning/sustaining electrode(Y). In the sustaining interval, a sustaining pulse having the same duty ratio of 1 is applied to the scanning/sustaining electrode(Y) and the common sustaining electrode(Z) as shown in FIG. 4.
In such a PDP driving method, a brightness difference is generated between sub-fields depending upon which sub-field is positioned between sub-fields. Specifically, gray level values 127 and 128 are a single gray level, but the gray level value 127 is a sum of the first to seventh sub-fields SF1 to SF7 at which a sustaining discharge is generated. On the other hand, the gray level value 128 generates the discharge only at the eighth sub-field(SF8). Accordingly, a brightness or gray level difference is generated at each sub-field to express a gray level value non-linearly. When a brightness difference between sub-fields is generated, a moving picture pseudo contour noise occurs. For instance, if the screen has been moved into the left side of the screen after the left half of the screen was displayed by a gray level value 128 and the right half of the screen was displayed by a gray level 127, then a white strip appears at the boundary portion between the gray level values 128 and 127. To the contrary, if the screen has been moved into the right side of the screen after the left half of the screen was displayed by a gray level value 128 and the right half of the screen was displayed by a gray level value 127, then a black stripe appears at the boundary portion between the gray level values 127 and 128.
In order to remove the pseudo contour noise, there have been one scheme of rearranging a sequence of sub-fields with the sustaining pulse having constant duty ratio and frequency and other scheme of dividing one sub-field to add one or two sub-fields to it. The pseudo contour noise may be reduced by the error diffusion method. However, such methods have drawbacks in that their implementation is very complicated and the brightness and gray level difference between sub-fields is still serious.
Accordingly, it is an object of the present invention to provide driving method and apparatus for a plasma display panel that is capable of performing a gray scale levels linearly.
In order to achieve these and other objects of the invention, a PDP driving method according to one aspect of the present invention includes the steps of differently setting duty ratios of sustaining pulses applied in a sustaining interval in each sub-field; and combining the sub-fields in a certain arrangement sequence.
A PDP driving method according to another aspect of the present invention includes the steps of differently setting frequencies of sustaining pulses applied in a sustaining interval in each sub-field; and combining the sub-fields in a certain arrangement sequence.
A PDP driving apparatus according to still another aspect of the present invention includes duty ratio controlling means for determining a duty ratio for each sub-field; and duty ratio compensating means for adjusting a duty ratio of a sustaining pulse for each sub-field under control of the duty ratio controlling means.
A PDP driving apparatus according to still another aspect of the present invention includes frequency controlling means for determining a frequency for each sub-field; and frequency compensating means for adjusting a frequency of a sustaining pulse for each sub-field under control of the frequency controlling means.